Method and apparatus for transporting and launching an offshore tower

ABSTRACT

A method and apparatus for transporting an offshore tower to a working site upon one or more articulated strings of freely pivotally connected flotation chambers. At a desired site, the flotation chambers are sequentially flooded to controllably lower the tower into the body of water. The flotation string may then be disconnected from the tower and controllably sequentially refloated for subsequent reuse.

United States Patent Inventor Joseph Benton Lawrence Houston, Tex.

Appl. No. 29,994

Filed Apr. 20, 1970 Patented Jan. 11, 1972 Assignee Brown & Root, Inc.

Houston, Tex.

METHOD AND APPARATUS FOR TRANSPORTING AND LAUNCHING AN OFFSHORE TOWER 14Claims, 14 Drawing Figs.

U.S. Cl til/46.5, 61/723, 114/.5, 114/435 Int. Cl E02b 17/02 E02c 5/00Field of Search 61/465, 46,

81, 82, 72.3, 52; l 14/.5 D, .5 F,43.5, 52

[56] References Cited UNITED STATES PATENTS 3,472,035 10/1969 Broussardet al. 6l/72.3 3,507,126 4/1970 Rochelle et al. 61/7213 3,036,438 5/1962Sims 6l/46.5 X FOREIGN PATENTS 625,728 l96l Italy 61/723 PrimaryExaminer-Jacob Shapiro Attorney-Burns, Donne, Benedict, Swecker & MathisABSTRACT: A method and apparatus for transporting an offshore tower to aworking site upon one or more articulated strings of freely pivotallyconnected flotation chambers. At a desired site, the flotation chambersare sequentially flooded to controllably lower the tower into the bodyof water. The flotation string may then be disconnected from the towerand controllably sequentially refloated for subsequent reuse.

PATENTEnJm 1 m2 3.633369 SHEETlUFS FIGZ JOSEPH BENTON LAWRENCEEMA/4100M. 9W

ATTORNEYS PATENTED JAN: 1 m2 SHEET 2 OF 5 PATENTEU mu 1 me I SHEET 3 or5 Q i A. w w m p Q 1 \m I l I I! III A. W g g f 1 K E of 27W i 8 M W E uT n 11111 m: N -m H w: m w n m 3 EM NN :5 A K w: N f u. zz: 552 55 8 w:w llllll l|v.|lII 6: Ti l mimmm 1m 3 633 369 SHEEI a UF 5 slrsaalsssPATENTED JANI 1 I972 SHEET 5 [IF 5 METHOD AND APPARATUS FOR TRANSPORTINGAND LAUNCI-IING AN OFFSHORE TOWER BACKGROUND OF THE INVENTION Thisinvention relates to a method and apparatus for transporting anderecting an offshore tower at a desired working site within a body ofwater such as for example a lake, sea or ocean.

More particularly, the invention relates to an improved launching vesseland launching process for safely and efficiently positioning a largeofishore tower upon the bed of a body of water. Towers have amultiplicity of applications in a marine environment, such as forexample supports for radar or sonar stations, light beacons, scientificmarine exploration labs and the like. Additionally, offshore towers arefrequently used in the oil industry in connection with drilling,producing and distributing operations.

Drilling for oil in oil or gas fields situated beneath the surface of abody of water has in the recent past become an extremely active andimportant segment of creativity in the oil industry. While in theinitial stages of development, exploration and drilling were conductedin locations of relatively shallow water depths from a few feet to 100or 200 feet, such as exists along the near shore portions of the Gulf ofMexico, it has more recently been the accepted practice to establishsites in water depths from a few hundred to 1,000 or more feet, such asexists along the Pacific coast continental shelf and in the Arcticregions.

In order to exploit mineral resources which exist below such asubstantial depth of water, tower designs which have been reliable andeffectively utilized in the past have undergone redesign for prolongedhigh stress, deep water use. In this connection offshore towers areenormous structures presenting truly significant engineering challengesnot only from an initial design aspect but from a subsequentconstruction, transportation and erection point of view.

At least one previously known method of transporting and launching arelatively shallow water tower comprises transporting a tower to adesired working site, resting upon a pair of pivotally connected barges.

One barge is considerably larger than the second and when ballasted willserve as a support in a jackknifing erection operation. In thisconnection hydraulic cylinders are coupled between the two barges topivot the smaller barge and the tower into an approximately verticalposture.

While such an apparatus and technique may be satisfactory for shallowwater and towers of relatively small size, it has been found that thisprocess is infeasible for most deep water applications.

Another method of transporting and erecting an offshore tower which hasbeen effectively utilized in deep water locations comprises segmentingthe tower legs with bulkheads into ballast compartments and floating thetower to an offshore site on the buoyant tower legs. At the work sitethe compartments are flooded to sink the tower to the bed of the body ofwater.

While this technique is frequently adequate, it has recently beendesirable to drill through the tower legs. It will be readily realizedthat flotation compartment bulkheads obstruct the free placement ofconductors within the legs at an offshore site and/or require intricateshipyard fabrication.

Further a lack of universal application or reuse often makes such aconcept of transportation and erection economically undesirable.

A further known method of transporting and launching offshore towerscomprises attaching one or more pontoons to the exterior of the towerstructure and floating the tower to a working site resting upon thepontoons, then releasing the pontoons to enable the tower to settle uponthe bed of the body of water. However, floats or pontoons attached to adrilling tower are under enormous loads. Releasing the pontoons from theweight of the tower immediately unleashes buoyancy forces correspondingto the previous weight of the supported tower with the resultant effectof an almost explosive throwing and thrashing of the flotation chambers.This violent action in conjunction with the enormous pontoon sizesrequired to support current deep water offshore towers renders theoperation extremely hazardous to personnel and equipment.

It would therefore be desirable to provide a safe and efficient methodand apparatus for transporting offshore towers of large dimensions to asuitable working site and controllably lowering the tower within thebody of water. Additionally, it would be advantageous to be able tosafely detach the apparatus from the tower so as not to interfere withdrilling operations and permit reuse in subsequent transport anderection operations. Further, it would be desirable to provide a methodand apparatus which would be universally applicable to a variety oftower designs and therefore economically attractive.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore a general object ofthe invention to provide a method and apparatus to obviate or minimizeproblems of the type previously described.

It is a particular object of the invention to provide a method andapparatus for controllably transporting and launching a deep wateroffshore tower within a body of water.

It is a further object of the invention to provide a method andapparatus for transporting and launching an offshore tower whereby theapparatus may be removed from the launched tower for reuse in subsequentoperations.

It is a still further object of the invention to provide a method andapparatus for launching an offshore tower which will minimize thehazards to equipment and personnel during the launching operation.

It is another object of the invention to provide an apparatus fortransporting and erecting an offshore tower which may be self-containedand remotely controlled.

It is still another object of the invention to provide a method andapparatus for transporting and erecting an offshore tower which willminimize the stress and load requirements placed upon the apparatus tothus minimize the possibility of failure while simultaneously minimizingthe structural design requirements.

It is yet another object of the invention to provide a method andapparatus for transporting and launching an offshore tower which isuniversal in application and may be readily adapted to accommodate aplurality of tower designs and configurations.

It is yet a further object of the invention to provide a method andapparatus for transporting and launching an offshore tower which willnot hinder subsequent drilling operations and will be economicallyattractive.

THE DRAWINGS Other objects and advantages of the present invention willbecome apparent from the following detailed description taken inconjunction with the accompanying drawings, wherein:

FIG. I is an isometric view of an offshore tower positioned within abody of water, having attached along a lateral surface apparatus fortransporting and launching a deep water offshore tower according to onepreferred embodiment of the invention, including two articulated stringsof flotation vessels freely pivotally connected at their ends;

FIG. 2 is a side elevational view of one of the flotation vessels, whichhas been partially broken away to disclose the interior thereof,according to one preferred embodiment of the invention;

FIG. 3 is a side elevational view of FIG. 2 disclosing one of theflotation vessels partially broken away to disclose the interior thereofand further illustrating clamps used to connect each of the flotationvessels to a lateral surface of an offshore tower;

FIG. 4 is a detailed view of a clamping arrangement according to oneembodiment of the invention;

FIG. 5 is a detailed view of a second clamping arrangement according toanother embodiment of the invention;

FIG. 6 is a schematic view of a portion of the control mechanismutilized with a flotation vessel as illustrated in FIGS. 2 and 3;

FIG. 7 is another schematicview of a control arrangement according toone embodiment of the invention; and

FIG. 8-14 disclose in a schematic array a preferred method oftransporting and erecting an offshore tower utilizing the articulatedstring of flotation chambers according to the invention.

DETAILED DESCRIPTION Referring now to the drawings, and moreparticularly to FIG. 1 thereof, there will be seen an offshore towerresting upon the bed 22 of a body of water 24 and extending above thesurface 26. The tower includes generally vertically legs 28 which extendfrom the bed to above the surface of the body of water. The legs areinterconnected at select locations along the length thereof byhorizontal braces 30 and sloping struts 32 which adds stability thereto.Positioned at the lower end of the tower is a sloping skirt arrangement34 resting upon the bed of the body of water to provide a widespreadsable base for enhancing the lateral stability of the tower design. Thespecific tower structure 20 per se does not form a part of thisinvention, but merely represents one of a multiplicity of currentlyutilized tower designs. Rather, releasably connected along the verticallegs 28 are articulated strings of buoyancy vessels 36 pivotallyconnected at their ends in tandem which serve to transport the tower 20to a preselected offshore site and erect the same in a controllablemanner in accordance with a preferred embodiment of the invention.

The articulated strings 36 may be interconnected in a mutually parallelposture by generally horizontal braces 42 and crossing struts 44. Theaxes of the strings 36 are held in a generally parallel posture withrespect to the central axis of the offshore tower 20.

The articulated strings 36 are composed of individual buoyancy vessels33 pivotally connected at their ends by hinge plate arrangements 40. Thehinge plate arrangements 40 permit the individual chambers to mutuallyfreely pivot for reasons which will become apparent hereinafter. Thebraces 42 and struts 44 as previously mentioned maintain the generallyparallel posture between adjacent individual flotation chambers 38making up the articulated string 36 and serve to prevent lateraltwisting displacement about the tower legs 28.

Turning now to FIGS. 2 and 3, there will be seen detailed views,partially broken away, of an individual flotation vessel 38. The vessel38 is fabricated with a generally cylindrical skin 46 which is closed atits ends by hemispherical caps 48 to form a watertight chamber. A ventvalve 50 is tapped into the upper end of the vessel and serves, in theopen posture, to permit the rapid ingress of ballasting fluid into theflotation vessel 38.

Each flotation vessel 38 is provided with a fore hinge plate 54 and anaft hinge plate 56. The hinge plate 54 is provided with a plurality ofcylindrical fingers 58 which serve to mate with compatibly spacedfingers 60 in the aft hinge plate 56 of a corresponding flotation vessel38. A pin may be intimately received through the mating fingers topivotally bind the flotation vessels in a freely pivotally connectedarticulated string. The hinge plates 54 and 56 are fixedly mounted tothe flotation vessel 38 by suitable tying brackets 59 having coped endsurfaces 61 for intimate engagement with the spherical end portions 48of the, flotation vessel. The coped end surfaces 61 may be fixedlywelded to the end spheres 48 to integrally attach the hinge plates 54and 56 to the outer skin of the flotation vessels 38.

In those instances where a pair of articulated flotation vessel strings36 are affixed to an offshore tower for the transportation and erectionthereof the strings are fixedly interconnected in a generally parallelposture by a plurality of generally horizontal braces 42. Further,crossing struts 44 are utilized to insure the generally parallelconfiguration of the flotation chambers under excessive loadingconditions. While it will be recognized that a single string of vessels36 may be adequate for many applications, in those instances where thepossibility of twisting of the strings 36 about the tower peripheryexists, a pair of interconnected strings is preferred.

Each of the flotation vessels 38 is independently clamped to a verticalleg 28 of the ofi'shore tower by one or more pivotal C-clamparrangements 62, as best seen in FIGS. 3, 4 and 5. A pair of bridgingbrackets 64 extend normally from the generally cylindrical skin 46 ofthe vessel in an upper and lower position. Pivotally connected by pinjunctions 68 at the free end of each bracket 64 are a pair of generallyC-shaped embracing arms 66. The arms 66 are so dimensioned as tointimately embrace a tower leg 28 and releasably attach the vessel 38thereto.

Referring now specifically to FIG. 4, there will be seen one embodimentof an actuation system which serves to control arms 66. Morespecifically, a pair of hydraulic cylinders 70 may be pivotallyconnected at one end to the bracket 64 as at 72. The cylinders 70 areprovided with axially reciprocating rams 74 which pivotally connect attheir free ends to lateral portions of the arms 66 as at 76. Fluid fromcontrol lines 78 and 80 serves to reciprocate the rams 74 within thecylinders and thus control the clamping movement of the arms 66.

An alternative embodiment for clamping flotation vessel 38 to anoffshore tower is specifically illustrated by FIG. 5. More specifically,the generally C-shaped arms 66 are provided at their outer ends with tabextensions 82 having one or more apertures therein. Conventionalexplosive fasteners 84, such as for example explosive bolts, arepositioned through the apertures to maintain the secure embracingrelationship of the arms 66 with a tower leg 28 until the fasteners 84are detonated.

Each flotation vessel 38 is provided in one preferred embodiment with aninternal compressed gas cylinder 86, which is fixedly positionedrelative to the cylindrical skin 46 by radially extending spoke brackets88.

The buoyancy of each flotation vessel 38 may be independentlycontrollable from a remote source by a system utilizing the internalcompression cylinder 86 in a manner schematically illustrated in FIG. 6.The compressed gas cylinder 86 is preferably provided at its upper endwith a blow valve comprising, for example, a direct acting four-wayspool valve 90. The valve 90 is normally biased by a spring 92 in aleft-hand mode, as viewed in FIG. 6, wherein the compressed gas cylinder86 is in normal communication with a plug 94. The plug maintains thescaled integrity of the cylinder 86 but permits rapid refilling of thegas cylinder at desired intervals. To accomplish this refillingoperation a port (not shown) must of course be fashioned through thevessel skin. This port may be easily rescaled, however, so that thevessel may be reused in a flotation capacity. A remotely controlledelectromechanical mechanism, such as for example a solenoid, may beselectively actuated which will serve to shift the spool valve 90 to arighthand posture, as shown in phantom. In this position the valve 90will connect the interior of the compressed gas cylinder to a checkvalve 98 and therethrough to the interior of the flotation vessel 38.

A ballast fill or jettisoning discharge valve 52 is positioned, aspreviously mentioned, in the lower hemispherical shell 48 of theflotation chamber 38. The valve 52 comprises a direct acting normallyclosed two-way sleeve valve being biased in a normally closed mode by aspring 100. An electromechanical mechanism 102, such as for example asolenoid, may serve to actuate the valve 52 to a left-hand posture, asviewed in FIG. 6. In this mode the interior of the flotation tank willbe directly connected with the ambient sea water environment and thevessel 38 will take water.

Integrally connected into the upper hemispherical shell 48 is a ventvalve 50 comprising a direct acting normally closed two-way valve,similarv to the previously discussed ballast fill or jettisoningdischarge valve 52. Like valve 52 the vent valve is provide with aspring bias 104 to normally maintain the valve in a closed posture orleft-hand mode, as viewed in FIG. 6. An electromechanical device 106,such as for example a solenoid, serves to shift the valve to aright-hand posture shown in phantom and connect the interior of theflotation vessel 38 through a check valve 108 to the ambientenvironment.

The electromechanical mechanisms 96, 102 and 106 may be electricallyoperated by connections, not shown, to a surface vessel or may each maybe provided with coded sonar responsive actuating mechanisms as desired.In any event each of the valves 50, S2 and 90 are designed to beindependently and selectively actuated from a remote location such as acontrol barge floating upon the surface of the body of water 24.

Referring now to FIG. 7 there will be seen an alternative control systemfor regulating the buoyancy of the articulated string of flotationvessels 36. More particularly, a supply of fluid, such as air underconstant pressure, is schematically represented by closure 110. It willbe understood that this supply may be mounted upon a control barge (notshown) with an umbilical cord composed of a plurality of lines runningto each flotation tank 38. The supply system 110 may comprise a motordriven compressor system or may be merely a large tank of compressed airmounted upon the vessel.

An air supply line 112 leads from the supply system 110 and is separatedby an open cross into a control line 114, a power line 116 and a clampactuation line 118.

The power line 116 runs to a manually controllable direct acting two-wayblow valve 120 and through a check valve 122 to the interior of theflotation vessel 38. The blow valve 120 is mounted adjacent a controlpanel positioned aboard the control vessel. The power line 116downstream of the check valve 122 branches into a remotely controllabledirect acting normally closed two-way vent valve 124 which may bemechanically operated by a spring biased piston and cylinder 126. Thevalve 124 in the open position connects the control line 116 downstreamof the check valve and thus establishes communication between theinterior of the vessel 38 and the ambient environment.

The lower hemisphere 48 of the flotation vessel 38 is tapped by aconduit which leads directly into a direct action normally closedtwo-way valve 128. Valve 128 may be controlled by a piston and cylinder130. The piston and cylinder 130 is spring biased such that the valve isnormally in a closed posture. In the open position, valve 128 leadsdirectly into the ambient environment and thus may be accurately termeda ballast fill or jettisoning discharge valve.

The vent valve 124 and ballast fill or jettisoning discharge valve 128are physically connected to the flotation vessel 38 and are remotelycontrolled by direct acting normally closed two-way valves 132 and 134,respectively. These valves are manually operable by a toggle switch andare connected adjacent the control panel mounted aboard the supportvessel. The valves 132 and 134 are further directly connected with thecontrol line 114 for selectively and controllably supplying air pressureto the valve actuating mechanisms 126 and 130.

The clamp actuation line 118 connects directly into a direct actingtwo-way valve 132 which is mounted adjacent the control panel and may bemanually operable by a toggle switch. The control valve 132 leadsdirectly into one of the two control lines 78 or 80 which connectdirectly with the vessel mounted cylinders 70. As previously discussedthese cylinders in conjunction with rams 74 to actuate the clamping arms66 to releasably embrace and clamp the flotation vessels 38 to the legs28 of an offshore tower 20.

While the above discussion referred to a single vessel 38 and itscontrol valves, additional control circuits may be fed from a branchline 136 to supply pressure for control valves as needed tor additionalvessels and an additional power and clamp actuation line 138 extends toserve a similar number of additional vessels in a manner as previouslydiscussed in connection with the single vessel 38 illustrated in FIG. 7.

While FIG. 1 discloses strings 36 of five flotation vessels 38 thenumber is merely representative and it will be appreciated that inactual operation more or less may be utilized. Further, each vessel 38is'substantially identical and thus individual vessels may be readilyadded or removed to accommodate a variety of offshore tower designs.Further, if one or more vessels 38 should become damaged or excessivelyworn, that vessel may be readily replaced without replacing the entirestring of vessels.

The sequencing and mode of operation of each of the above-describedelements will be discussed more fully hereinafter in conjunction withthe overall mode of operation of the flotation and launch vessel.

METHOD OF TRANSPORT, LAUNCHING AND RECOVERY Referring now specificallyto FIGS. 8-14, there will be seen in a schematic array, a generallysequential depiction of transporting an offshore tower to a selectedsite, controllably erecting the tower upon the bed of the body of waterand retrieving the transport and launch apparatus.

More particularly and referring to FIG. 8 there will be seen an offshoretower 20 horizontally supported along the surface 26 of a body of water24 by at least one articulated string of buoyancy chambers 36 pivotallyconnected at their ends in tandem. The tower in its horizontally floatedposture may be towed to a desirable offshore site by a control barge140. In the transportation posture, each of the individual flotationvessels 38 is substantially void of water and the vent, blowing andballast fill or discharge valves are all in a closed posture.

Upon reaching a desired site, as illustrated in FIG. 9, the individualflotation chambers 38 are sequentially ballasted beginning with thelowermost vessel 144 and progressing toward the uppermost chamber 146 insequential order to induce an upending of the tower 20 into the body ofwater 24. In order to induce the entry of ballast or water into thechamber 38, the ballast valve is opened along with a vent valve whilethe blow valve is maintained in a closed posture. It will readily berealized that the vent valve permits water to freely enter through theballast valve without simultaneously displacing air through this valvethus insuring a more easily controllable ballast operation.

The individual vessels 38 are designed so that upon being freely filledwith water they are approximately neutrally buoyant. In this connectionit may be necessary to establish one or more air chambers (not shown)within the interior of each vessel 38 or a compressed gas cylinder 86attached to each of the vessels may be so dimensioned to provide thedesired neutral buoyancy upon full flooding.

During the erecting operation the vent and ballast fill or dischargevalves are held in an open posture to permit the free ingress and egressof water such that differential pressures between the interior and theexterior of each flotation vessel 38 is maintained approximately zerowith any depth of water. This permits the skin of the vessel 38 to befabricated with less thickness than would be possible if a substantialpressure differential were allowed to build up particularly with respectto the bottom vessel 144.

Referring now to FIG. 10, the individual flotation vessels have beenballasted or flooded to neutral buoyancy, and the offshore tower 20being positively buoyant is free to bob in a generally vertical posturewithin the body of water 24.

After the offshore tower 20 is thus righted, the articulated string offlotation vessels 36, as best seen in FIG. 11, are simultaneouslyreleased from the offshore tower by the separation of the clamp arm 66all along the lateral surface of the offshore tower. As previouslydiscussed, the release operation may be produced by a variety ofmechanisms and modes of operation. However, two methods which have beenfound to be satisfactory are explosive bolts 84 or hydraulic rams 74.Due to the neutral buoyancy of the individual flotation chambers 38during this separation operation, there will be a minimum tendency toproduce high shear forces in the C- clamp couplings 62 and along thelateral legs 28 of the offshore tower. The thus released articulatedstring of buoyancy vessels 36 freely hang in a vertical posture withinthe body of water 24 along the lateral surface of the tower.

In order to controllably recover the string 36 for future use, theindividual buoyancy vessels 38 are sequentially blown beginning with theuppermost vessel M6 progressing toward the bottom vessel M4. During theblowing operation, the vent valve is closed, the blowing valve is openedand the ballast discharge valve remains open. After the individualchambers 38 are blown of their fluid and reach the surface, the ballastdischarge valve and blowing valve may be closed.

Simultaneously, as best seen in FIGS. iii-l3, as the blowing operationproceeds, the control barge M connected to the uppermost vessel 146 isnavigated away from the tower 20. This initially tips the uppermostvessel M6 away from damaging contact with the tower .20 while theremaining vessels 38 hang in a generally vertical posture also away fromthe tower.

As the individual chambers 38 are blown and reach the surface, they eachpivot about their hinge connection 40 while the remaining lower ballastvessels hang generally vertical in the water. The movement of thecontrol barge 40 away from the tower location and the sequential blowingof the individual vessels 38 insure a smooth resurfacing of theflotation vessels as the articulated string of buoyancy vessels 36 istowed away from the erection site.

Referring to FIG. 14, following the recovery of the articulated stringof flotation vessels 36 the tower legs 28 may be flooded to set theoffshore tower upon the bed 22 of the body of water 24. The tower may bethen pinned to the subsea bed 22 by piles.

The tower thus erected may serve to stably support a platform M2 abovethe surface of the body of water for a multiplicity of uses aspreviously discussed.

SUMMARY OF SIGNIFICANT ADVANTAGES Thus it will be seen that the presentinvention provides an improved method and apparatus for transporting andlaunching a deep water offshore tower.

Particularly significant is the provision of a plurality of freelypivotally connected flotation chambers of uniform dimensions which mayreadily be replaced if one becomes worn or damaged and which furtheradmits to assembling of as many chambers as is necessary to accommodatevarying structural dimensions of offshore towers.

Another important feature of the invention is the self-contained natureof one preferred embodiment which minimizes the requirement forexcessive support equipment and which may be remotely controlled.

Another advantage of the invention is the provision of parallel stringsof flotation chambers which prevent corkscrewing or rotating of thevessel strings about the tower during the transport or launchoperations.

Another significant advantage of the invention is the provision ofcontrollably launching the tower and rapidly and controllably retrievingthe transport and launch apparatus once the tower is in an erectposition which minimizes hazards to personnel and equipment in theimmediate working vicinity and which further frees the apparatus forsubsequent operations.

A significant method aspect of the operation includes the provision offlooding to meet neutral buoyancy conditions of the flotation chambersand the simultaneous release of all of the chambers from the towerstructure, thus minimizing or eliminating shearing stresses which wouldbe created if the chambers were not neutrally buoyant or were releasedfrom the tower in a nonuniform manner. Further, the sequential floodingof the flotation chambers provides a high degree of control whichminimizes the tendency of the tower to thrash about in the water. Inaddition, the maintenance of the ballast fill or jettisoning dischargevalve in an open posture during the raising and lowering of theflotation vessels insures that an excessive pressure differential willnot build up across the vessel skin.

Another significant advantage of the invention is the provision of thefreely coupled articulated flotation chambers which may be sequentiallyblown, beginning with the chamber nearest the surface, and thus may beorderly removed from the immediate vicinity of the previously rightedtower while the chambers remaining submerged will tend to hang in avertical posture, thus minimizing the possibility of underwater bumpingand potential damage to the tower.

Although the invention has been described with reference to preferredembodiments, it will be appreciated by those skilled in the art thatadditions, modifications, substitutions, deletions and other changes notspecifically described may be made which will fall within the purview ofthe appended claims.

What is claimed is:

H. An offshore tower transport and launching apparatus comprising:

a first plurality of generally hollow elongate flotation vessels, eachvessel having a longitudinal axis and said vessels being pivotallyconnected in substantially axial alignment for connection to the lateralsurface of an offshore tower whereby the longitudinal axis of theoffshore tower is substantially parallel to the aligned axes of theelongate flotation vessels;

a second plurality of generally hollow elongate flotation vessels, eachvessel having a longitudinal axis and said vessels being pivotallyconnected in substantially axial alignment for connection to the lateralsurface of an offshore tower whereby the longitudinal axis of theoffshore tower is substantially parallel to the aligned axes of theelongate flotation vessels;

means for fixedly interconnecting corresponding vessels of said firstplurality of flotation vessels with said second plurality of flotationvessels in a generally parallel posture;

means for releasably connecting said first and second plurality offlotation vessels to the lateral surface of the offshore tower;

means for selectively admitting fluid into each of said flotationvessels to submerge said vessels and the offshore tower within the bodyof water;

means for simultaneously disconnecting in a submerged posture each ofsaid flotation vessels from the lateral surface of the offshore tower;and

means for selectively jettisoning fluid from the interior of each ofsaid flotation vessels to induce the ascent of said vessels from asubmerged posture in the body of water.

2. An offshore tower transport and launching apparatus as defined inclaim 1 and further comprising:

means connected to each of said flotation vessels for establishing agenerally neutrally buoyant state of each of said flotation vessels uponsaid vessels being flooded.

3. An offshore tower transport and launching apparatus comprising:

a plurality of generally uniform submergible flotation vessels pivotallyconnected in tandem for transporting on a body of water an offshoretower to a desirable offshore work site and for submerging with theoffshore tower at the work site to position the offshore tower in anerect posture within the body of water;

means for admitting fluid into each of said flotation vessels tosubmerge said flotation tanks within the body of water;

means for releasably disconnecting in a submerged posture each of saidflotation vessels from the lateral surface of the offshore tower; and

at least one chamber of compressed gasfixedly connected to each of saidgenerally uniform flotation vesselsand having a selectively operablecontrol means connecting the interior of said flotation vessel and saidat least one compressed gas chamber for controllably jettisoning fluidfrom said flotation vessel.

4. An offshore tower transport and launching apparatus as defined inclaim 3 wherein:

said at least one chamber of compressed gas is positioned within theinterior of said uniform flotation vessel.

5. An offshore tower transport and launching apparatus as defined inclaim 3 wherein:

said at least one chamber of compressed gas connected to said generallyuniform flotation vessel is dimensioned to provide neutral buoyancy ofsaid flotation vessel when said flotation vessel is flooded. 6. Anoffshore tower transport and launching apparatus comprising:

an articulated string of freely pivotally connected flotation vesselsadapted to ferry an offshore tower to a drilling site; means forreleasably connecting each of said flotation vessels to a lateralsurface of the offshore tower; means for selectively flooding each ofsaid flotation vessels thus permitting said offshore tower to sink intothe body of water; and a high pressure chamber positioned within theinterior of each of said flotation vessels and having at least oneselectively controlled aperture therein for providing communication fromwithin the pressure chamber to the region between said pressure chamberand :he shell of said flotation vessel. 7. An offshore tower transportand launching apparatus as defined in claim 6 and further comprising:

at least another articulated string of freely pivotally connectedflotation vessels as defined in claim 6 and fixedly connected in agenerally parallel posture with respect thereto. 8. A method oftransporting and erecting an offshore tower comprising the steps of:

floating the offshore tower to an offshore site upon at least onearticulated string of pivotally connected flotation vessels connectedalong a lateral surface thereof; sequentially flooding each of saidflotation vessels beginning with the vessel attached nearest to thebottom of the offshore tower to permit said offshore tower to descendwithin the body of water; disconnecting said flotation vessels from thesubmerged offshore tower; and sequentially blowing said flotationvessels beginning with the vessel nearest the surface of the body ofwater to induce said flotation vessels to rise to the surface. 9. Amethod of transporting and erecting an offshore tower as defined inclaim 8 wherein:

said flotation vessels are simultaneously disconnected from thesubmerged offshore tower. 10. A method of transporting and erecting anoffshore tower as defined in claim 8 and further comprising the step of:

simultaneously with said step of sequential blowing towing said freelypivoted articulated string of flotation vessels away from the submergedtower. 11. A method of transporting and erecting an offshore tower asdefined in claim 8 and further comprising the step of:

maintaining the flooding valve of each flotation vessel in the openposition during the sequential flooding and blowing operations tominimize the pressure differential on the flotation vessels walls. 12. Amethod of transporting and erecting an offshore tower as defined inclaim 8 wherein:

said step of sequentially flooding each of said flotation vesselsproceeds only to the neutral buoyancy point of each of said flotationvessels. 13. A method of transporting and erecting an offshore towercomprising the steps of:

floating the offshore tower to an offshore site carried upon at leastone articulated string of freely pivotally connected flotation vesselsconnected along a lateral surface thereof; sequentially flooding each ofsaid flotation vessels to generally the point of neutral buoyancybeginning with the vessel attached nearest to the bottom of theofi'shore tower to permit said offshore tower to descend within the bodyof water; disconnecting said flotation vessels simultaneously from thesubmer ed offshore tower; sequentla y blowing the said flotation vesselsbeginning

1. An offshore tower transport and launching apparatus comprising: a first plurality of generally hollow elongate flotation vessels, each vessel having a longitudinal axis and said vessels being pivotally connected in substantially axial alignment for connection to the lateral surface of an offshore tower whereby the longitudinal axis of the offshore tower is substantially parallel to the aligned axes of the elongate flotation vessels; a second plurality of generally hollow elongate flotation vessels, each vessel having a longitudinal axis and said vessels being pivotally connected in substantially axial alignment for connection to the lateral surface of an offshore tower whereby the longitudinal axis of the offshore tower is substantially parallel to the aligned axes of the elongate flotation vessels; means for fixedly interconnecting corresponding vessels of said first plurality of flotation vessels with said second plurality of flotation vessels in a generally parallel posture; means for releasably connecting said first and second plurality of flotation vessels to the lateral surface of the offshore tower; means for selectively admitting fluid into each of said flotation vessels to submerge said vessels and the offshore tower within the body of water; means for simultaneously disconnecting in a submerged posture each of said flotation vessels from the lateral surface of the offshore tower; and means for selectively jettisoning fluid from the interior of each of said flotation vessels to induce the ascent of said vessels from a submerged posture in the body of water.
 2. An offshore tower transport and launching apparatus as defined in claim 1 and further comprising: means connected to each of said flotation vessels for establishing a generally neutrally buoyant state of each of said flotation vessels upon said vessels being flooded.
 3. An offshore tower transport and launching apparatus comprising: a plurality of generally uniform submergible flotation vessels pivotally connected in tandem for transporting on a body of water an offshore tower to a desirable offshore work site and for submerging with the offshore tower at the work site to position the offshore tower in an erect posture within the body of water; means for admitting fluid into each of said flotation vessels to submerge said flotation tanks within the body of water; means for releasably disconnecting in a submerged posture each of said flotation vessels from the lateral surface of the offshore tower; and at least one chamber of compressed gas fixedly connected to each of said generally uniform flotation vessels and having a selectively operable control means connecting the interior of said flotation vessel and said at least one compressed gas chamber for controllably jettisoning fluid from said flotation vessel.
 4. An offshore tower transport and launching apparatus as defined in claim 3 wherein: said at least one chamber of compressed gas is positioned within the interior of said uniform flotation vessel.
 5. An offshore tower transport and launching apparatus as defined in claim 3 wherein: said at least one chamber of compressed gas connected to said generally uniform flotation vessel is dimensioned to provide neutral buoyancy of said flotation vessel when said flotation vessel is flooded.
 6. An offshore tower transport and launching apparatus comprising: an articulated string of freely pivotally connected flotation vessels adapted to ferry an offshore tower to a drilling site; means for releasably connecting each of said flotation vessels to a lateral surface of the offshore tower; means for selectively flooding each of said flotation vessels thus permitting said offshore tower to sink into the body of water; and a high pressure chamber positioned within the interior of each of said flotation vessels and having at least one selectively controlled aperture therein for providing communication from within the pressure chamber to the region between said pressure chamber and the shell of said flotation vessel.
 7. An offshore tower transport and launching apparatus as defined in claim 6 and further comprising: at least another articulated string of freely pivotally connected flotation vessels as defined in claim 6 and fixedly connected in a generally parallel posture with respect thereto.
 8. A method of transporting and erecting an offshore tower comprising the steps of: floating the offshore tower to an offshore site upon at least one articulated string of pivotally connected flotation vessels connected along a lateral surface thereof; sequentially flooding each of said flotation vessels beginning with the vessel attached nearest to the bottom of the offshore tower to permit said offshore tower to descend within the body of water; disconnecting said flotation vessels from the submerged offshore tower; and sequentially blowing said flotation vessels beginning with the vessel nearest the surface of the body of water to induce said flotation vessels to rise to the surface.
 9. A method of transporting and erecting an offshore tower as defined in claim 8 wherein: said flotation vessels are simultaneously disconnected from the submerged offshore tower.
 10. A method of transporting and erecting an offshore tower as defined in claim 8 and further comprising the step of: simultaneously with said step of sequential blowing towing said freely pivoted articulated string of flotation vessels away from the submerged tower.
 11. A method of transporting and erecting an ofFshore tower as defined in claim 8 and further comprising the step of: maintaining the flooding valve of each flotation vessel in the open position during the sequential flooding and blowing operations to minimize the pressure differential on the flotation vessels walls.
 12. A method of transporting and erecting an offshore tower as defined in claim 8 wherein: said step of sequentially flooding each of said flotation vessels proceeds only to the neutral buoyancy point of each of said flotation vessels.
 13. A method of transporting and erecting an offshore tower comprising the steps of: floating the offshore tower to an offshore site carried upon at least one articulated string of freely pivotally connected flotation vessels connected along a lateral surface thereof; sequentially flooding each of said flotation vessels to generally the point of neutral buoyancy beginning with the vessel attached nearest to the bottom of the offshore tower to permit said offshore tower to descend within the body of water; disconnecting said flotation vessels simultaneously from the submerged offshore tower; sequentially blowing the said flotation vessels beginning with the vessel nearest the surface of the body of water to induce said string of flotation vessels to rise to the surface; and simultaneously towing said at least one articulated string of freely pivotally connected flotation vessels away from the submerged tower.
 14. A method of transporting and erecting an offshore tower as defined in claim 13 and further comprising the step of: maintaining the flooding valve of each flotation vessel in the open position during the sequential flooding and blowing operations to minimize the pressure differential on the flotation vessels walls. 